The present invention relates to semiconductor memory devices and, more specifically, to flash memory devices.
There is an increasing demand for electrically erasable and programmable semiconductor memory devices which are capable of retaining their stored data even without power supplies. In addition, there is a demand for high-capacity semiconductor memory devices. Flash memory devices can provide high capacity even without power supplies and retain their stored data even when their power supplies are interrupted. For this reason, flash memory devices have been widely used in electronic devices (e.g., portable electronic devices) whose power supplies may be suddenly interrupted.
Semiconductor memory devices have increased in capacity. Capacity is proportional to integration density of a semiconductor memory device. According to so-called “Hwang's Law”, semiconductor memory devices have doubled in density every year. i.e., increasingly higher-capacity semiconductor memory devices can be fabricated. However, the need for increased data capacity is increasing with the increase in active data exchange resulting from advances in communication networks. It is therefore desirable to provide even higher density semiconductor memory devices to meet these capacity needs.